A method of calculating surface evapotranspiration by separately
including the effects of vegetation and atmospheric evaporative demand
under the condition of nonlimiting soil moisture is presented. A
literature survey is conducted to determine the effects of plants on
evapotranspiration.
To represent the atmospheric evaporative demand, the original
potential evaporation equation of Penman (1948) is utilized and then
modified to include the effect of atmospheric stability using turbulent
exchange coefficients formulated by Louis et al. (1982). The
original and modified Penman expressions are compared for different
asymptotic cases. Using boundary layer data from the Wangara experiment
(Clarke et al., 1971), the diurnal variations of the original
and modified Penman equations are compared. The daily total potential
evaporation using linearized and integrated forms of the original and
modified expressions are also compared. Finally, the nonlinear effects
of averaging both the original and modified expressions are
examined. It is found that including the diurnal variations of stability
in the modified expression causes large hourly differences with
the original expression under non-neutral conditions, while daily
averages of the two compared fairly well. The diurnal variation of
the surface moisture flux appears to be much larger than predicted
by the original Penman expression. However, the original Penman expression
remains a reasonable estimate of the 24-hour total potential
evaporation. / Graduation date: 1983
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/29054 |
| Date | 10 December 1982 |
| Creators | Ek, Michael Bryan |
| Contributors | Mahrt, Larry J. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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